(i) Technical Field
The present invention relates to a semiconductor laser device and a method for controlling a semiconductor laser.
(ii) Related Art
It is known that, in a case where an optical signal having small line width and having high power is input into an optical fiber, SBS (Stimulated Brillouin Scattering) may be occurred when a value based on the line width and the power exceeds a threshold value. Thus, the optical signal may get dramatically degraded. A control technology of placing a given amount of wavelength dispersion on an optical output having a small line width (SBS suppression technology) is developed as a method of suppressing signal degradation caused by the SBS.
On the other hand, a structure, in which a SG-DBR (Sampled Grating Distributed Bragg Reflector) and a SG-DFB laser (Sampled Grating Distributed Feedback laser) are coupled to each other, is known as a wavelength tunable laser of which oscillation wavelength is variable.
Japanese Patent Application Publication No. 2007-048988 discloses a wavelength tunable laser in which a CSG-DBR (Chirped Sampled Grating Distributed Bragg Reflector) is coupled to the SG-DFB laser instead of the SG-DBR for increase in performance.
A wavelength tunable laser having the CSG-DBR as a tuning element uses a vernier-shaped selectable wavelength determined by the CSG-DBR. It is preferable that wavelength selectivity of the CSG-DBR is not broken down, if the SBS suppression technology is adapted to the wavelength tunable laser.